Conventionally, as a seat reclining apparatus for a vehicle for tilting a seatback relative to a seat cushion, there has been known an apparatus disclosed in JP2003-000379A, for example. The seat reclining apparatus for a vehicle comprises an upper plate (2) having an internal tooth (25a) and a lower plate (1) on which a plurality of poles (50, 60) are movably mounted in a radial direction. As a cam (40) provided about a rotational shaft rotates, the internal tooth of the upper plate and external teeth (54, 64) of the pole are engaged or released with or from each other, so that the rotation of the upper plate relative to the lower plate is restricted or allowed. Due to this structure, the rotation of the seatback relative to the seat cushion is restricted or allowed, so that the seatback can be adjusted and kept at a tilted angle preferable and desired for a passenger to seat.
Further, in a recessed portion (25) forming the internal tooth of the upper plate, a recessed portion (26) having an inner diameter smaller than the diameter of the recessed portion (25), concentric with the recessed portion (25), and recessed into deeper depth than the recessed portion (25) is provided. The recessed portion (26) is formed with a first stopper portion (27a) and a second stopper portion (27b) projecting radially inward from the inner peripheral surface thereof at an interval with a predetermined angle. On the other hand, one specific pole (50) is formed with a projection (51). As a result that the end surface at one side or the other side of the projection in the circumferential direction about the rotational shaft is brought into contact with the opposed surface of the first or the second stopper, the rotational angel of the upper plate relative to the lower plate, that is, the rotational angle of the seatback relative to the seat cushion is kept at a predetermined angle.
Further, the recessed portion (26) is formed with a restricting portion (28) projecting radially inward from the inner peripheral surface by the length of projection smaller than the first and second stopper portions within a predetermined angular range between the first and second stopper portions located at the side where the one specific pole is disposed. In the state where the projection of the pole is opposed to the restricting portion in the radial direction, the end surface of the projection located radially outward is brought into contact with the opposed surface of the restricting portion. In this state, the radial movement of the pole for engagement with the upper plate is restricted, and the rotation of the upper plate relative to the lower plate is kept in a permissive state. That is, the restricting portion defines an angular range in which the permissive state of the rotation of the upper plate relative to the lower plate is kept as it is, that is, an angular range in which the permissive state of the rotation of the seatback relative to the seat cushion is kept as it is. Thus, the rotational angle of the seatback relative to the seat cushion is maintainable in a range except for the angular range described above.
However, according to the seat reclining apparatus disclosed in JP2003-000379A, two kinds of poles (50, 60) are required, inevitably resulting in an increase in the number of kinds of parts. Further, the permissive state of the rotation of the upper plate relative to the lower plate is kept only by the engagement between the upper plate and one specific pole (50). The remaining pole (60) is controlled via a cam (40) which engages with the pole (60) by inserting a projection (47) into a cam hole (56) of one specific pole. Therefore, the remaining pole is movable in a radial direction within a clearance created between the pole and the projection (47) inserted into the cam hole (66). In this state, for example, even in the permissive state of the rotation of the upper plate relative to the lower plate, the external tooth (64) may interfere with the internal tooth of the upper plate.
A need thus exists to provide a seat reclining apparatus for a vehicle capable of suppressing an increase in the number of kinds of parts.